Polyester-based spandex filament

ABSTRACT

A polyester-based spandex filament or film is provided. The filaments when used swim-wear fabrics provide the fabrics with increased resistance to mildew-induced degradation. The filaments are formed from a spandex derived substantially from a poly(1,2-dimethyl-1,3-propylene 1,12-dodecanedioate) glycol having no more than 15 milliequivalents of glycol acidity per kilogram of glycol, which glycol is capped with an organic diisocyanate and then chain-extended with an aliphatic diamine.

This is a division of application Ser. No. 913,406, filed Sept. 30,1986.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an elastic filament formed from a spandexpolymer derived from a hindered polyester, an organic diisocyanate andan aliphatic diamine chain extender. The invention particularly concernssuch a filament wherein the polyester is derivable from2,2-dimethyl-1,3-propane diol (neopentyl glycol) and 1,12-dodecanedioicacid. The spandex filaments of the invention have improved resistance todegradation by mildew attack.

2. Description of the Prior Art

Elastic filaments of polyester-based spandex polymer can be preparedfrom a hydroxyl-terminated polyester which is capped with an organicdiisocyanate and then reacted with an aliphatic diamine chain extender.The polyester forms what is called the "soft segment" of the polymer;the diisocyanate and diamine form the so-called "hard segment". Thepolymer can then be formed into filaments or films by known techniques.For example, filaments may be formed by dry spinning. Many suchpolyester-based spandex filaments are known. Some have enjoyedconsiderable commercial success, but their value could be furtherenhanced by certain improvements. For example, in swim-wear fabrics,although such filaments usually have adequate resistance to attack byswimming-pool chlorine, the filaments often degrade because of mildewattack. Accordingly, an object of the present invention is to provide apolyester-based spandex filament that has satisfactory elastic andtensile characteristics and satisfactory chlorine-resistance, but thatalso resists degradation caused by mildew attack.

Many hydroxyl-terminated polyesters made from α,ω-dicarboxylic acids andglycols have been disclosed for use in making the polyester-basedspandex polymers. Generally, a preference is disclosed for acids thatcontain ten or fewer carbon atoms. However, none of the disclosuresaddress the problem of mildew resistance or specifically mentionpoly(2,2-dimethyl-1,3-propane dodecanediote) as a soft segment of apolyester-based spandex filament.

For example, U.S. Pat. No. 3,009,762 (Kohrn et al) and No. 3,009,765(Slovin et al) disclose such hydroxyl-terminated polyesters derived fromglycols and saturated organic dicarboxylic acids, the glycols and acidseach having from 4 to 20 carbon atoms. These patents disclose thatpreferred polyesters precursors have a molecular weight of 1500 to 3000and an acid value of less than 1. An acid value of 1 is equal to aglycol acidity of about 17.6 milliequivalents per kilogram (meq/kg).Among the polyesters specifically mentioned, though not exemplified, isa hindered polyester, poly(neopentyl sebacate).

U.S. Pat. No. 3,097,192 (Schilit) discloses elastic filaments ofpolyester-based spandex polymers and states that when the ester functionis hindered, as with polyesters made with 2,5-hexane diol or2,2-dimethyl-1,3-propane diol, the hydrolytic stability of the polymeris enhanced. In Examples II and IX, Schilit discloses a polyester-basedspandex filament made with a polyester soft segment formed from sebacylchloride and 2,2-dimethyl-1,3-propane diol. However, the tensile andelastic characteristics of the disclosed filaments are clearly in needof significant improvement.

Among the many other patents that disclose hydroxyl-terminatedpolyesters for segments of spandex filaments are U.S. Pat. Nos.2,621,166 (Schmidt), 2,956,961 (Kibler et al), 3,211,701 (Muller et al),3,481,905 (Weiden et al), 3,496,144 (Kunde et al), 3,506,617 (Collardeauet al) and 3,907,863 (Voss).

From a practical standpoint, some degradation of the spandex filamentfrom mildew attack can be tolerated without it being objectionable tousers of fabrics containing the filaments. However, the utility of thepolyester-based spandex filaments would be much improved by increases intheir mildew resistance.

SUMMARY OF THE INVENTION

The present invention provides an improved elastic filament or filmformed from a spandex polymer that has a hindered polyester soft segmentand a hard segment derived from an organic diisocyanate and an aliphaticdiamine chain extender. The improved filament has enhanced mildew andchlorine resistance and comprises a soft segment made substantially froma poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate) glycol having aglycol acidity of no more than 15 milliequivalents per kilogram,preferably no more than 10 and most preferably no more than 5 meq/kg.The hindered polyester preferably has a molecular weight in the range of2300 to 2700, most preferably in the range of 2400 to 2600.

In a process of the invention, the improved filament or film is formedfrom spandex polymer made by capping the polyester with an organicdiisocyanate, preferably an aromatic diisocyanate, most preferablymethylene bis(4-phenyl isocyanate) and then chain-extending theresultant isocyanate-terminated polyester with an aliphatic diamine,preferably a mixture of ethylene diamine and 1,3-diaminocyclohexane.

Preferred as-spun spandex filaments of the invention have a set of lessthan 25%, an unload power of at least 0.027 gram per effective denier(gped) and a break elongation of at least 400%. After being heat-set,filaments of the invention have, in addition to improved mildewresistance and satisfactory chlorine resistance, tensile and elasticcharacteristics that include a set of no more than 25%, an unload powerof at least 0.036 gped and a break elongation of at least 300%.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be more readily understood by reference to thedrawing which presents a graph of the heat-set unload power and percentset of a filament of the invention as a function of the glycol acidityof a hydroxyl-terminated poly(2,2-dimethyl-1,3-propylene1,12-dodecanedioate) used to form the soft segment of the filamentspandex polymer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein, the term "fiber" includes staple fibers and/orcontinuous filaments. "Spandex" has its usual definition; that is, along chain synthetic polymer that comprises at least 85% by weightsegmented polyurethane. The terms "soft segment" and "hard segment"refer to specific portions of the spandex polymer chains. The softsegments are the polyester portions of the segmented polyurethanepolymer and the hard segments refer to the portions of the polymerchains that are derived from the reaction of an organic diisocyanatewith a diamine chain extender. Glycol acidity, as used herein, refers toend groups, such as acid end groups, of the polyester glycol precursorwhich do not react with organic diisocyanates under conventionalurethane-forming conditions, such as those illustrated in the examplesbelow. The isocyanate end group content of a polymer may be referred toas the NCO content.

As noted, the spandex polymer for use in the present invention comprisesa soft segment made substantially from a poly(2,2-dimethyl-1,3-propylene1,12-dodecanedioate)glycol having a certain maximum glycol acidity. Theterm, "substantially made from", is intended to include in the glycol asmall portion (e.g., up to as much as 25%) of copolymerized units ofother aliphatic diacids and/or glycols, so long as these other acidsand/or glycols do not detrimentally affect the mildew resistance,tensile and elastic properties of the final filaments or films.

In accordance with the present invention, a polyester-based spandexfilament of improved mildew resistance is provided when a particularhindered polyester soft segment is included in the spandex polymerchains. The particular soft segment is poly(2,2-dimethyl-1,3-propylene1,12-dodecanedioate).

For ease of manufacture, the polyester soft segment usually is preparedfrom the corresponding hydroxyl-terminated polyester. Conventionalmethods, such as those described in R. Hill, "Fibres from SyntheticPolymers", Elsevier Publishing Co., New York, p. 144ff (1953), aresatisfactory for synthesizing the polyester that will subsequently formthe soft segment of the spandex polymer of the fibers. These methodsinclude: (a) direct esterification of an acid (i.e., in this case,1,12-dodecanedioic acid) and a glycol (i.e., in this case,2,2-dimethyl-1,3-propane diol); (b) ester interchange between the glycoland an ester of the acid; (c) reaction of the glycol with thecorresponding acid chloride; and (d) reaction of the diacetate of theglycol with the acid or its ester.

To prepare spandex polymer for the filaments or films of the invention,the soft-segment precursor, most usually in the form of a polyesterdiol, has a molecular weight in the range of 1,700 to 3,000, preferablyin the range of 2,200 to 2,700, and most preferably in the range of2,300 to 2,600. In addition, the polyester diol must have a glycolacidity of no more than 15, preferably no more than 10, and mostpreferably less than 5 meq/kg. As shown in the drawing, which is derivedfrom the data of Example 2, low glycol acidity in the polyester diolresults in superior properties in the final spandex filament. Inparticular, lower permanent set and higher unload power are obtained.

To form the spandex polymer for the filaments or films of the invention,the above-described polyester soft-segment precursor is reacted (or"capped" as it is sometimes called) in a conventional manner with anexcess of an organic diisocyanate to form an isocyanate-terminatedpolyester which is then chain-extended with an aliphatic diamine.Suitable diisocyanates are methylene bis(4-phenyl isocyanate),tolylene-2,4-diisocyanate, p-phenylene-2,6-diisocyanate and the like,with the first-mentioned diisocyanate being preferred. The cappingreaction preferably is carried out so that the isocyanate end groupcontent of the capped polyester is in the range of 2.2 to 3.3 weightpercent, most preferably 2.4 to 3.1. The preferred ranges of NCOcontents result in a preferred combination of elongation, unload powerand set in the final spandex filaments. Suitable aliphatic diamine chainextenders include ethylene diamine ("EDA", also known as 1,2-diaminoethane), hydrogenated meta-phenylene diamine ("HMPD", also known as1,3-diaminocyclohexane), propylene diamine, mixtures thereof and thelike. The preferred chain extender is a mixture of EDA and HMPD,particularly preferred in a weight ratio of 80 to 20 parts, or 90 to 10parts, respectively.

The polymerization reactions are generally carried out in an inertsolvent, such as dimethylacetamide, dimethylformamide or the like. Thethusly prepared spandex polymer can then be dry spun into filaments orformed into films, usually from the same solvent as was used for thepolymerization. Dry-spun filaments or formed films can then be heat-setby maintaining them for 2 to 10 minutes at a temperature in the range of145° to 165° C. while stretched to 1.5 to 3.5 times their originallength and then being immersed in boiling water in a relaxed conditionfor at least 20 minutes. Of course, higher setting temperatures forshorter times (e.g., at 195° C. for 30 seconds) can be employedsatisfactorily.

The filaments and films of the present invention have an unexpectedlygood resistance to mildew. In addition, the filaments resist degradationdue to swimming-pool chlorine, have excellent hydrolytic stability,especially in acid environments, and have satisfactory elastic andtensile properties. As a result, filaments of the present invention areparticularly useful for swim-wear fabrics.

The resistance of polyester-based spandex filaments and films tochlorine-induced degradation can be further improved by using a spandexformed by from the poly(2,2-dimethyl-1,3-propylene1,12-dodecanedioate)glycol employed in the spandex of the presentinvention and the functionally non-aromatic diisocyanates andfunctionally non-aromatic diamines disclosed by Altau and Stiehl in U.S.Pat. No. 3,994,881, such as tetrachloro-(meta and/or para)-xylylenediisocyanate, tetrachloro-(meta and/or para)-xylylene diamine, or thelike.

The following test procedures were used in the Examples and Comparisonsbelow for measuring various parameters and properties.

Glycol acidity, which is defined herein as the concentration of ends,such as acid ends, in the polyester precursor which do not react withisocyanates under conventional urethane-forming conditions, such asthose illustrated in the examples below. The glycol acidity of thehydroxyl-terminated polyester was measured by the method ofASTM-1638-67T and is reported herein in milliequivalents per kilogram ofthe hyrdoxyl-terminated polyester.

The molecular weights reported herein are number average molecularweights of the polyester diols. Each was determined from the hydroxylnumber of the polyester diol, which was measured by theimideazolepyridine catalyst method described by S. L. Wellon et al,"Determination of Hydroxyl Content of Polyurethane Polyols and OtherAlcohols", Analytical Chemistry, Vol. 52, No. 8, pp. 1374-1376 (July1980).

The NCO content of isocyanate-capped hindered polyester was measured bythe method of S. Siggia, "Quantitative Organic Analysis via FunctionalGroup", 3rd Edition, Wiley & Sons, New York, pages 559-561 (1963).

Relative viscosity of the spandex polymer was determined with a 0.5%concentration solution of the polymer in N,N-dimethylacetamide solvent.Relative viscoscity is defined as the ratio of the flow times ofsolution to solvent at 25° C. in a capillary viscometer.

Strength and elastic properties of the spandex filaments were measuredin accordance with the general method of ASTM D 2731-72. Threefilaments, a 2-inch (5-cm) gauge length and a zero-to-300% elongationcycle were used for each of the measurements. "Unload Power" (i.e., thestress at an elongation of 100%) and "Set" were measured after thesamples had been cycled five times at an constant elongation rate of800% per minute and then held at the 300% extension for half a minuteafter the fifth extension. Stress, on unloading from this lastextension, was measured and expressed as grams per effective denier at100% elongation. At the end of the fifth cycle and after the sample hadbeen allowed to recover for a half minute, the measured length of thesample was then used to calculate the set, which was expressed as apercentage of the original length of the sample. The percent elongationand tenacity at break were measured on the sixth extension cycle.Tenacity is reported in grams per denier or grams per dtex. Effectivedenier is the denier of the filament at 100% elongation. Resistance toattack by chlorine was measured by the method described in U.S. Pat. No.4,340,527, column 4, lines 7 through 25. The method involves immersing atest yarn, while extended to 150% of its original length, in a waterbath maintained at a temperature of 22° C., at a pH of 7.5 by additionof hydrochloric acid, and at an active chlorine concentration of 3 partsper million by addition of sodium hypochlorite solution. After theexposure, the yarn is dried and its physical properties are measured, asdescribed in the preceding paragraph. After-exposure yarn propertieswere then compared to the properties before exposure to determine thatamount of degradation.

Resistance to attack by mildew was measured by the general method ofASTM D-1924-70. An aqueous dispersion of aspergillus niger spores wasemployed. The test was performed on single-knit (four feed hosierymachine) hosiery panty fabric made with 50-denier, 17 filament nylon ascompanion fibers to the spandex test filaments. The spandex filamentswere knitted in every fourth course without plaiting with the nylon.Before mildew testing, the fabric was washed with one half cup oflaundry detergent in a home laundry washing machine set for a normalwash and rinse cycle, followed by drying in a home laundry dryer set fora permapress cycle. Square samples of the fabric measuring 3 inches (7.6cm) on each side were then fastened under light tension over cylindricalpolystyrene dishes. The samples were then innoculated with the aqueousspore dispersion. Days to first failure were then measured. Failure wasrecorded as the time at which a hole was evident in the fabric sample.In each test, a similar control fabric made with commercialpolyester-based spandex filaments was exposed under the same conditions.The comercial polyester-based spandex yarn was Type-128 "LYCRA" spandex,available from E. I. du Pont de Nemours and Company. The polymer of thecommercial yarn was formed from a 3,400-molecular-weight polyesterglycol that was derived from the reaction of a 60/40 ethyleneglycol/1,4-butanediol mixture with adipic acid and then capped withmethylene bis(4-phenyl isocyanate) and extended with ethylene diamine.

EXAMPLE 1

This example illustrates the manufacture of an elastic filament of theinvention made from a spandex polymer having apoly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate) soft segment.Compared to commercial filaments in which the dicarboxylic acid portionof the soft segment is derived from adipic acid and a glycol portionthat is not hindered, the filaments of this example have surprisinglysuperior resistance to chlorine and mildew attack.

A hydroxy-terminated polyester having a molecular weight of 2499 and aglcol acididity of 3.6 meq/kg was prepared from 1,12-dodecanedioc acidand 2,2-dimethyl-1,3-propane diol. A weight of 82.8 grams of thispolyester glycol was mixed with one drop of phosphoric acid and 5 ml ofcyclohexane. The mixture was stirred while being heated to a temperatureof 85° C. in a nitrogen-blanketed vessel. After thirty minutes ofheating, the mixture was allowed to cool to 40° C. Then, the polyesterglycol was capped with an aromatic diisocyanate by adding 17.2 grams ofmethylene bis(4-phenylisocyanate) (MDI) to the mixture and heating themixture at 90° C. for two hours. The capped polyester had a 3.04%concentration of isocyanate groups. After being allowed to cool to about25° C., the mixture was dissolved in 110.6 grams ofN,N-dimethylacetamide. The isocyanate-capped polyester, while still insolution, was then reacted with 70.9 grams of a mixture of aliphaticdiamine chain extenders and a chain terminator in N,N-dimethylacetamidecarrier. The mixture of aliphatic diamines consisted of 0.796 gram of1,3-diaminocyclohexane (HMPD), 1.675 grams of 1,2-diaminoethane (EDA),0.184 gram of diethylamine and 69.245 grams of N,N-dimethylacetamide. Ahalf gram of 1,1-bis(6-methyl-3-tertiary-butyl-4-hydroxyphenyl)butanestabilizer was added to the resultant viscous polymer solution. Thepolymer had a relative viscosity of 1.6.

Elastic filaments were formed from the polymer solution by conventionaldry spinning techniques. Filaments of 66 denier (73 dtex) were wound upat a speed of 150 yards per minute (137 meters/min).

The filaments had the following satisfactory tensile characteristics:

    ______________________________________                                        Fifth cycle unload power                                                                            0.029 g/edtex                                           at 100% elongation                                                            Fifth cycle set       24%                                                     Break tenacity (sixth cycle)                                                                        0.72 gram/dtex                                          Break elongation      482%                                                    ______________________________________                                    

Other filaments made substantially according to the procedures of thisexample were tested for mildew and chlorine resistance by the testprocedures described hereinbefore. The tests were performed on as-spunfilaments and on filaments that had been heat set for 3 minutes at 150°C. while being held at an elongation of 150% and then immersed inboiling water in a relaxed condition for 30 minutes. The filaments alsowere tested for hydrolytic stability by immersing the filaments in waterof pH 3 at 70° C. for one hour and then measuring the tenacity of thefilaments. In each of these tests, the results on the filaments of theinvention were compared to those obtained with a commercial non-hinderedpolyester-based control yarn (i.e., Type-128 "LYCRA" spandex) testedunder the same conditions.

The test samples made according to this example exhibited four to tentimes greater resistance to mildew attack than did the commercialpolyester-based spandex yarns. Furthermore, the samples with thecommercial yarn control exhibited a much higher severity of failure(i.e., many failure sites) at the recorded time of first failure, incontrast to the fabrics having yarns of the invention which exhibitedonly one small hole at time of recorded failure.

In the chlorine resistance tests, the samples made in accordance withthis example exhibited about the same or somewhat better resistance tochlorine attack than did samples containing the commercial controlspandex yarn.

In the hydrolytic stability test, the samples of commercial spandexfilaments lost all of their tenacity, whereas those of the exampleretained more than 40% of their tenacity.

EXAMPLE 2

This example illustrates how filament mechanical properties are affectedby the free acidity of the poly(2,2-dimethyl-1,3-propanedodecanedioate)glycol used to manufacture hindered polyester-basedspandex filaments of the invention and demonstrates the requirement fora glycol acidity in the polyester glycol of no more than 15 meq/kg.

A series of spandex filaments was made according to the generalprocedures of Example 1 with a soft segment derived frompoly(2,2-dimethyl-1,3-propane dodecanedioate)glycol having a molecularweight of 2,400. As in Example 1, the glycol was capped with MDI to forman isocyanate-terminated polyester having a 3.1% concentration of NCOgroups which was then chain extended with an 80/20 EDA/HMPD mixture. Aseries of the polyester glycols, each glycol having a different freeacidity, was prepared by heating the glycol with a small amount of waterfor different times. The thusly prepared spandex polymers were dry-spuninto filaments, as in Example 1. The filaments then were heat set at150° C. for 3 minutes while be held at a 200% elongation and thenimmersed in boiling water for 30 minutes while in a relaxed condition.The heat-set and boiled-off filaments had the tensile and elasticproperties listed below. Note that the first three samples are of theinvention; the last two are comparisons, outside the invention.

    ______________________________________                                        Glycol Filament Characteristics                                               acidity         %     unload    tenacity                                                                             elonga-                                meq/kg dtex     set   g/edtex   g/dtex tion, %                                ______________________________________                                        4.4    43       21    0.041     0.97   336                                    11.1   40       23    0.037     1.01   354                                    14.9   43       24    0.032     0.77   349                                    19.9   49       23    0.030     0.90   373                                    26.7   47       25    0.029     0.69   351                                    ______________________________________                                    

The data given above, as well as other such data, show the desirabilityof low glycolacidity in the polyester glycol used to prepare the softsegment of the spandex filaments. Low acidity generally results infilaments having lower set and higher unload power. The attached drawinggraphically illustrates these results.

I claim:
 1. A process for making a spandex filament or film, wherein inthe presence of an inert organic solvent2,2-dimethyl-1,3-propane diol isreacted with 1,12-dodecanedioic acid to form a hydroxyl-terminatedpolyester having a molecular weight in the range of 2,200 to 2,700 and aglycol acidity of no more than 15 meq/kg, the thusly formed polyester isreacted with an organic diisocyanate to form an isocyanate-terminatedpolyester having an isocyanate end-group content in the range of 2.2 to3.3%, the isocyanate-terminated polyester is then chain-extended with analiphatic diamine to provide a viscous spandex polymer solution having arelative viscosity in the range of 1.5 to 1.9, and the polymer solutionis formed into filaments or film.
 2. A process according to claim 1,wherein the polyester is formed with a molecular weight in the range or2,300 to 2,600 and a glycol acidity of no more than 10 meq/kg and theisocyanate-terminated polyester is formed with an NCO content in therange of 2.4 to 3.1%.
 3. A process according to claim 1 or 2 wherein theorganic diisocyanate is methylene bis(4-phenyl isocyanate) and thediamine chain-extender is a mixture of ethylene diamine and1,3-diaminocyclohexane.
 4. A process according to claim 1 or 2 whereinthe polyester is formed with a glycol acidity of no greater than 5meq/kg.
 5. A process according to claim 1 or 2 wherein the polymersolution is spun into filaments having a set of less than 25%, aretractive power of at least 0.027 gped and a break elongation of atleast 400% and the thusly spun filaments are then heat set to increasethe retractive power to at least 0.036 gped while maintaining the breakelongation at no less than 300%.